sed (Stream Editor)

sed is a powerful stream editor used to perform basic text transformations on an input stream (a file or input from a pipeline). It is commonly used for text substitution, deletion, and insertion.

Basic Syntax

sed [options] 'script' [input-file]

Commonly Used Options

-e script: Add the script to the commands to be executed.
-f script-file: Add the contents of the script-file to the commands to be executed.
-i[SUFFIX]: Edit files in place (makes backup if SUFFIX supplied).
-n: Suppress automatic printing of pattern space.
-r: Use extended regular expressions in the script.
-s: Treat files as separate rather than as a single continuous long stream.
-u: Load minimal amounts of data from the input files and flush the output buffers more often.

Common Commands

s/pattern/replacement/flags: Substitute pattern with replacement.
d: Delete pattern space.
p: Print pattern space.
a\ text: Append text after the current line.
i\ text: Insert text before the current line.
c\ text: Replace the current line with text.
y/source/dest: Transliterate characters in the pattern space.

Flags for `s` Command

g: Global replacement.
p: Print the line if a replacement was made.
w file: Write the result to a file.
number: Replace only the numberth occurrence.

Examples

Substitute Text

Replace the first occurrence of "foo" with "bar" in each line:

sed 's/foo/bar/' input.txt

Replace all occurrences of "foo" with "bar" in each line:

sed 's/foo/bar/g' input.txt

Delete Lines

Delete lines containing "foo":

sed '/foo/d' input.txt

Delete the first line of the file:

sed '1d' input.txt

Print Lines

Print lines containing "foo":

sed -n '/foo/p' input.txt

Print the first 10 lines of the file:

sed -n '1,10p' input.txt

Insert and Append Text

Insert "Hello" before the first line:

sed '1i\Hello' input.txt

Append "World" after the last line:

sed '$a\World' input.txt

Replace Entire Line

Replace lines containing "foo" with "bar":

sed '/foo/c\bar' input.txt

Transliterate Characters

Replace all occurrences of "a" with "A" and "b" with "B":

sed 'y/ab/AB/' input.txt

In-Place Editing

Replace "foo" with "bar" in the file and save changes:

sed -i 's/foo/bar/g' input.txt

Using a Script File

Create a script file script.sed with the following content:

s/foo/bar/g
/hello/d

Run sed with the script file:

sed -f script.sed input.txt

Using Extended Regular Expressions

Replace all digits with "X":

sed -r 's/[0-9]/X/g' input.txt

Conclusion

sed is a versatile tool for text processing and can be used for a wide range of tasks, from simple substitutions to complex text manipulations. Understanding its options and commands allows for efficient and powerful text editing directly from the command line.

Last modified: 14 December 2024